In a variety of fields of foodstuffs, pharmaceuticals, miscellaneous goods and so on, there have been widely employed bags (or bags with snap zippers) which can be opened and closed optionally with belt-like snap zippers (fasteners), each comprising a pair of male and female portions, provided in opening regions of the bags. Various methods of manufacturing such bags with snap zippers have been proposed. For example, there are known methods of; (1) extruding a tubular film together with a snap zipper, comprising a pair of male and female portions, through an extrusion die; and (2) manufacturing a tape with a snap zipper in advance and then bonding the tape to a base film, which forms a bag body, by hot welding (melting for adhesion) or an adhesive. See Japanese Patent Laid-Open No. 56-42640, No. 61-231220, No. 61-232111, No. 61-232112, No. 63-232114 and No. 63-42849, and Japanese Patent Publication No. 62-40185, for example.
However, the former method (1) is restricted in its application to only common versatile products consumed in large quantities for the reasons of a limitation in the sorts of usable resin, difficulty in application to a base film of the multilayer type, lack of adaptability to various sizes, and difficulty in printing, etc. Therefore, the latter method (2) has been employed, particularly, in the field of packing high-class goods by taking advantage of its flexible adaptation to versatile combinations of tapes with snap zippers and base films. But, such tapes with snap zippers can be applied to those base films formed of similar type resin alone, and materials currently used for the tapes with snap zippers are only low-density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride (PVC), etc. Thus, the latter method (2) also has a disadvantage in that it is not adapted for bag bodies formed of metal foils which are frequently being employed these days, some limitation is experienced in the actual combination of materials selected, and hence the method cannot always be applied to all sorts of base films.
In order to improve the hot-melting adhesion, therefore, it has further been proposed to use mixed resin of crystalline propylene copolymer (Japanese Patent Laid-Open No. 59-49249), and to use a multilayered snap zipper (Japanese Patent Publication No. 51-43054).
Because of a reduction in the hot-welding temperature, such improved snap zippers are effective, for example, in preventing deformation of the snap zippers and restraining the occurrence of failed appearance of the hot-welded portions to some extent. However, those snap zippers present no basic solution to the problem inasmuch as they will not allow free selection of all sorts of materials.
Furthermore, the following drawbacks are associated with use of higher-temperature fusible resin such as polypropylene; a. poor hot-melting adhesion, b. difficulty in continuous process and reduction in the manufacture speed (because the need of both hot pressing and cooling necessitates a batch process in practice); c. adverse effects due to heat exerted on base films and snap zippers (i.e., edge drop, deformation of snap zippers, occurrence of pin holes, etc.); and d. difficulty in achieving the small size of the manufacture apparatus. In addition, the bonding method using an adhesive accompanies problems below; e. complicated process; f. need of a specific adhesive; g. insufficient adhesion in the case of employing such materials as ill compatible with the adhesive used; and h. contamination and hygienic trouble due to outward spread of the adhesive.
Meanwhile, conventional bags with snap zippers are completely enclosed by their sealed ends before opening, and are cut in regions between the snap zippers and the sealed ends when used, followed by opening the snap zippers. Such cutting has hitherto been made by using scissors, or tearing the bag by hands from a notch formed on the side edge of the region to be cut. However, the latter cutting method has a disadvantage that the bag cannot be torn neatly along a straight line.
For the above reason, there are proposed several methods capable of linearly tearing the bags by hands without using any tools such as scissors. Included in these methods are, for example, the techniques of; i) forming a perforated line as a tear line; ii) making thicker an outerside portion of an innerside film where a snap zipper is formed, forming a cut-out line in that thicker portion, and then laminating an outerside film on the innerside film to thereby fabricate a bag with a snap zipper (see Japanese Utility Model Laid-Open No. 52-18254); iii) forming a non-hot melting layer on the innerside of a film in the region near a snap zipper, where a cut line is to be formed, and carrying out hot welding through the non-hot melting layer in a perforation manner to thereby fabricate a bag with a snap zipper (see Japanese Patent laid-Open No. 58-171347); iv) forming a recessed cut-out portion 70, which extends to the base film 10, in a tape 13 having a snap zipper thereon, as shown in FIG. 21; and v) forming a half cut-out portion 70 in a tape 13 having a snap zipper thereon, as shown in FIG. 22.
Among the conventional methods of manufacturing bags with snap zippers as set forth above, the method i) of forming a perforated line makes the bag less airtight due to the presence of perforations, and may open the bag for some reason during transportation or other situations where it should be kept in a sealed state. The method ii) of forming a cut-out line in the innerside film in advance and then laminating an outerside film on the innerside film enables the innerside film formed with the cut-out line to be torn neatly, if it is left alone, i.e., before lamination. But, after bonding the innerside film to the base film by hot melting, there is a fear that the cut-out line may be filled with the melted resin upon application of heat and the bag may become hard to tear open along the cut-out line. The method iii) of forming a cut line by hot-welding in a perforation manner can improve the sealability to some extent, but still has disadvantages that the sealability is not perfect and the process is complicated. The method iv) of forming a recessed cut-out portion has disadvantages that the torn line tends to curve unintentionally rather than a neat linear one, and a tape separate from the tape with a snap zipper requires to be hot-welded. The final method v) has disadvantages that the torn line also tends to curve unintentionally rather than a neat linear one, and the tape has a large width, variations in thickness and a tendency to curl in the widthwise direction, which invites some difficulty in the melting operation.
Further, since the bag fabricating process and the bagging process have been separately treated in the prior methods, it is inevitable for the entire packing process to be complicated, have a low efficiency because of difficulties in accomplishing continuous and automatic processing and to be unsuitable for bagging and packing of products in mass production. As a method of solving that problem, therefore, there has also been proposed a so-called pillow packing that is intended to perform both the bag fabrication process and the bagging process simultaneously.
However, the foregoing prior methods of manufacturing and filling bags with snap zippers, even in the case of employing the pillow packing, could not avoid the problems. a-h as stated above, because films with snap zippers have been obtained through bonding by hot melting or using an adhesive with any number of methods.